The working of fibrous material in the known refiners most often is carried out in an ineffective manner. A significant portion of the energy input to these refiners is used for transporting the fibrous material through the refiner, wherein friction and heat losses occur which do not result in the alterations of the fibrous material which are required for developing the pulp quality and for making the refining process effective. It is therefore apparent that the energy consumption is higher than that required for achieving the desired mechanical working; i.e., the desired pulp quality.